To simplify the manufacturing process, it is known to provide picture tube glass pans with markings, which permit recognition of the glass pan type, or the glass pan itself. The glass pan forms that part of a picture tube, which faces the viewer after it has been installed.
A known way to realize such markings is to place a label on the outside of the respective glass pan. To that effect, according to U.S. Pat. No. 4,374,551, a label with printed information is glued to the glass pan. In view of the temperature processes which the glass pan undergoes during manufacture, it is easy to see that such a solution does not guarantee reliable and permanent marking of picture tube parts. For this reason, DE 38 25 846 also indicates an adhesive label, which has an identification made of glass solder. If this label is glued to the outside of the glass pan, and the pan then undergoes a temperature process, the identification combines with the glass of the pan to form a permanent marking that is no longer removable.
However, if a number of different types of picture tubes are manufactured in a production line, it is considered a disadvantage to use labels, because a corresponding number of labels must be kept on hand for the different types of tubes, and it would be extremely expensive to produce such labels immediately before they are combined with the glass pan. Furthermore, for the latter reason, the variety of information on each label is limited.
According to another state of the art patent (U.S. Pat. No. 4,327,283), the marking of picture tube parts takes place in such a way, that at least one glass frit area is formed on the outside of the respective picture tube part. Depending on the process, the marking is then either made in the form of a machine-readable bar code in that area, and the respective area is then fritted to the glass pan, or vice versa. The formation of the bar code is such, that the application of suitable measures on predetermined areas of the additionally formed area causes the applied glass frit material to be partially removed. The measures that are suitable for removing the glass frit material are indicated as mechanical and chemical processes, including laser technology.
Although this process provides for individual identification of each glass pan, it is considered a disadvantage that this type of marking always requires that at least one layer must be produced on the glass pan in several work steps, which is not required for the picture tube production itself. As pointed out in this regard by U.S. Pat. No. 4,600,630, for reasons of readability, it is necessary to cover the bar code marking produced in U.S. Pat. No. 4,327,283, with a special layer to protect it from contamination.
As was shown in tests performed by the applicant, a direct marking is not realizable, i.e. one that is worked into the surface of the screen glass, because, as also indirectly confirmed by U.S. Pat. No. 4,327,283, it leads to an unacceptable weakening of the glass screen-pan, which is under considerable load in the subsequent installed condition.
For that reason, the invention has the task of introducing markings of picture tube parts, whose manufacture does not require additional layers or materials beyond the production of the respective picture tube part, and which are additionally protected against outside influences.
Another task of the invention is to introduce a process for the production of markings of picture tube parts, which permits to manufacture identification marks of picture tube parts in a very simple process that is safe and protected against outside influences.